a. Field of the Invention
The present invention relates to a process for the removal of nitrogen oxides (hereinafter referred to as NO.sub.x) from industrial waste gases such as from boilers, heating furnaces and incinerators which contain said oxides in conjunction with sulfur oxides (hereinafter referred to as SO.sub.x) by catalytic reduction of the nitrogen oxides utilizing ammonia as the reducing agent. The invention provides a novel process for effectively removing NO.sub.x from the waste gas on a commercial scale utilizing a catalyst which manifests high initial activity even in the presence of SO.sub.x, and retains this activity for a long period of time.
B. Description of the Prior Art
In recent years, the removal of NO.sub.x as well as that of SO.sub.x has become an important task in view of the mounting public issue of air pollution. No completely effective commercial method has yet been developed.
Various processes have been proposed. Of these processes, the most promising from the practical point of view is the process which effects selective catalytic reduction by use of ammonia as the reducing agent. This method uses metals of the platinum family and their oxides as catalysts.
In the reaction system in which SO.sub.x is present, however, such catalysts rapidly lose activity because of the poisonous effect of SO.sub.x so that continuous, extended operations cannot be performed. This problem manifests itself with systems containing 1000 to 2000 ppm of SO.sub.x.